The present invention relates generally to rodless pneumatic cylinders.
The term xe2x80x9crodless cylinderxe2x80x9d generally refers to a cylinder which does not use a piston rod. Such cylinders use little longitudinal space, and avoid the problems associated with cylinder piston rods, such as bending, rod surface damage, etc. Rodless cylinders have been generally well-received in the marketplace, particularly for long-stroke applications.
Rodless cylinders are known, for example, which include a slide table (or carriage) supported on a cylinder body. The slide table is connected by a coupler member to a piston reciprocating within a bore in the cylinder body. The coupler member extends through a longitudinal slot in the cylinder body to connect the slide table to the piston. A fluid such as air is directed through inlet and outlet ports on the cylinder body to move the piston back and forth along the longitudinal length of the body. The slide table is supported on at least one surface of the cylinder body, and moves in conjunction with the piston. Appropriate seals at both ends of the piston, at each end cap, and along the slot, prevent the fluid from escaping from the cylinder body. If machinery or workpiece components are fixed to the table, the movement of the components can be accurately controlled by the introduction of air into the cylinder body and the movement of the piston and the slide table.
Various cylinder designs have been developed in an attempt to improve the movement of the slide table under various load conditions, to minimize the size and reduce the number of components, and to reduce the manufacturing and assembly costs of the cylinder.
Certain cylinder designs are shown for example in U.S. Pat. No. 5,279,207. One design illustrated in FIG. 10 of this patent shows a slide table supported on a cylinder body by first and second pairs of holding mechanisms. Each holding mechanism includes a pair of guide members fixed to the slide table which are moveable against a pair of synthetic resin members fixed to the cylinder body. The holding mechanisms support the slide table under both vertical and horizontal loads, and allow the slide table to slide smoothly against the cylinder body.
The guide members of the holding mechanisms are disclosed as including guide rollers which are rotatable on rods fixed to the table, while the synthetic resin members are disclosed as including rail-shaped members mounted in grooves formed in channels along the entire length of the cylinder body. It is also disclosed to coat the surfaces of the channels with a synthetic resin film or hard alumite film instead of using the synthetic resin members. In FIG. 18, synthetic members are also shown for the guide members; while in FIG. 20, a guide roller-type of guide member is shown for one of the pairs of guide members, while a synthetic resin member is shown for the other of the pairs of guide members. In any case, the first and second holding mechanisms are shown as being separate components, separately connected to either the slide table and/or the cylinder body, and each appears to require separate manufacturing and assembly steps. All of this increases the over-all cost of the cylinder.
U.S. Pat. No. 5,305,682 show cylinder designs with similar separate holding mechanisms as in U.S. Pat. No. 5,279,207. U.S. Pat. No. 5,311,810 combines the guide roller-type of guide member with a linear guide member having ball bearings. U.S. Pat. Nos. 4,664,020 and 4,891,908 show wedge-shaped guide strips fixed to the slide table and slidingly received in guide grooves in the cylinder body. U.S. Pat. No. 5,317,957 shows a pair of wedge-shaped guide members fixed to the slide table which receive the pointed end of a pair of wedged-shaped guides fixed to the cylinder body. It is believed some of these cylinders can have certain performance issues, as well as additional assembly and manufacturing costs.
Another important factor in manufacturing a rodless cylinder is the piston design. Some references disclose complex piston designs which appear to require numerous components, and manufacturing and assembly steps. This can, again, increase the overall cost of the rodless cylinder.
In light of the above, Applicants believe there is a continual demand for new and unique rodless cylinders which provide for the accurate and smooth positioning of a slide table along a cylinder body for the movement of machine components and workpieces, which are operable under various load conditions, and which are easy to manufacture and assemble to reduce the over-all cost of the cylinder.
The present invention provides a new and unique rodless cylinder which positions a slide table along a cylinder body for the movement of machine components and workpieces. The rodless cylinder includes a bearing structure which incorporates few parts, provides for the smooth and accurate movement of the slide table on the cylinder body, and is easy to manufacture and assemble. The rodless cylinder also includes a piston structure which likewise is easy to manufacture and assemble. A rodless cylinder constructed according to the principles of the present, improves the movement of the slide table under various load conditions, minimizes the size and reduces the number of components, and reduces the manufacturing and assembly costs associated with the cylinder.
According to the present invention, the bearing structure includes a pair of generally V-shaped bearing members, preferably formed from a synthetic resin, which are interposed between the slide table and the cylinder body. Each bearing member includes first and second longitudinally-extending sidewalls, interconnected by a longitudinally-extending end wall. The slide table includes a pair of channels, with each channel facing generally downwardly and outwardly from the cylinder body. Each channel closely receives and retains a respective bearing member, which thereby also face generally downwardly and outwardly. The bearing members are retained in the channels in the slide table by a pair of end wipers fixed to the ends of the slide table. The cylinder body includes a pair of sidewalls which extend longitudinally along the length of the body on either side of the longitudinal slot in the body. The outer ends of the sidewalls have a wedge shape (in cross-section) and are generally directed inwardly toward each other. The wedge-shaped distal ends are received within the V-shaped bearing members supported in the channels of the slide table to allow the slide table to move smoothly and accurately along the cylinder body.
The V-shaped configuration of the bearing members allows smooth and accurate movement of the slide table under various load conditions. Horizontal and vertical loads are easily compensated by the location and V-shaped structure of the bearing members. Each bearing member, being formed in one piece, is also easy to manufacture and assemble with the cylinder body. The bearing members can also be easily slid into their respective channels before the end wipers are attached to the slide table. At least one of the bearing members is adjustable by a wedge bar, which is moveable by adjusting one or more adjustment screws on the slide table.
The piston for the rodless cylinder preferably comprises a pair of identical piston portions, which are retained together by a yoke member and coupled as a complete assembly to the slide table by the yoke member and a coupler member. The piston portions each have a complete piston head, and a body portion half, which is axially overlapped with the body portion half from the other piston portion to form a complete piston body. Rod magnets are received through corresponding holes in the piston body portions and the yoke to allow position sensing. The piston portions are each easy to manufacture (preferably molded from a resin material) and to assemble with the yoke.
The yoke member of the piston assembly extends through the longitudinal slot in the cylinder body, and is connected by the coupler member directly to the slide table. A disk-shaped portion of the coupler member is received within a press-fit in a circular opening in the lower surface of the slide table to allow limited off-axis movement of the slide table with respect to the piston assembly. The coupler member allows moment loading of the slide table and linearity deviations without compromising the uniform motion of the slide table along the piston body.
An inner sealing band is guided through the piston body while an outer-sealing band is guided between the coupler member and the slide table. The sealing bands fluidly seal the longitudinal slot and prevent contaminants from entering the cylinder bore during movement of the piston assembly. The sealing bands are connected by the use of band clamps and appropriate fasteners to the end caps of the cylinder body.
The invention as described above, improves the movement of the slide table under various load conditions, minimizes the size and reduces the number of components for the rodless cylinder, and reduces the manufacturing and assembly costs associated the cylinder.